1. Field of the Invention
This invention relates to an adaptor for use in a single lens reflex camera system with interchangeable photo-taking lenses of different F numbers, and more particularly to an adaptor attachable to and detachable from the body of a presently available interchangeable lens mount and capable of providing information representing the full open F number of the interchangeable lens in the form of a coded digital signal for a digitalized camera.
2. Description of the Prior Art
The prior art provides a single lens reflex camera system, with a series of interchangeable lenses of different full open aperture value of F number. The light metering mechanism of the exemplary camera is operated with a photosensitive element positioned to receive light from a scene being photographed through the interchangeable lens associated with the camera for determining an exposure value. This light metering of the so-called TTL type is characterized in that when the photo-taking lens is interchanged with a change in full open F number, (1) the photosensitive element produces a different output despite of the fact that the level of brightness of the scene remains unchanged, because the light metering is effected always at the full open aperture; and (2) the amount of change of the light intensity on the light-receiving surface of the photosensitive element does not coincide with the change of the light intensity on the focal plane (film surface), because the exit pupil position is shifted. In order to insure that the exposure control system of the camera cooperating with such a photosensitive element produces the proper exposure value with high accuracy and reliability regardless of the change in full open F number therefore, it is necessary to render the exposure control system responsive to information representing the full open F number of the associated interchangeable lens by a suitable compensating means.
An example of the conventional design features of such compensating means is that the individual interchangeable lenses are provided with respective signal producing pins of different length depending upon the full open F number and arranged, upon selective attachment of the interchangeable lenses to a common camera body, to control the position of a signal receiving member cooperating with the exposure control system of the camera in such a manner that information in the form of a displacement of the signal receiving member by a length proportional to the full open F number of the associated interchangeable lens is factored into an exposure value.
In transmitting information of the full open F number from the associated interchangeable lens to the exposure control system in the camera body, however, the use of such a signal producing pin with the signal receiving member gives rise to a possibility of creating a relatively large information shift error, because it is practically impossible to manufacture a production run of interchangeable lenses with signal producing pins affixed to the lens mounts economically, while holding all of the dimensions of the signal producing pins to specific values. Further, the provision of the signal receiving member between the signal producing pin and the exposure control system constitutes another source of information shift error. From the standpoint of assuring high accuracy and reliability and which the exposure control system is rendered responsive to the full open F value of the associated interchangeable lens, therefore, it is very disadvantageous to employ the analog type signal transmission mechanism.
On the other hand, in recent years digital signal processing techniques have been increasingly used in photographic cameras, wherein the computation of an exposure value representing an effective aperture value or exposure time, the display of the determined exposure value, and the control of the exposure determining mechanism including the diaphragm and the shutter are carried out by use of digital circuit means. Such a digitalized camera when adapted for use with interchangeable lenses having signal producing pins is required to have additional means for converting the analog information of the full open F value to a digital one. This signal converting process constitutes still another source of information shift error.
In order to eliminate the above mentioned drawbacks, one solution has been proposed for a digital type signal transmission mechanism in U.S. Pat. No. 3,782,261, entitled "Data Transmission Device for Use with Interchangeable-Lens-Camera" in which the camera body is provided with a uniform circular array of data transmission elements arranged on an annular surface of the camera, each of which is biased towards a projected position in which it sticks out of the camera mount annular surface, but can be pushed into a retracted position, while the interchangeable lens mount is provided at its corresponding annular surface with one or more arcuate slots adapted to receive loosely selected data transmission elements when the lens is mounted in its final position on the camera, whereby the mounting of the lens on the camera is effected with the result that selected data transmission elements are received in the slot or slots and thus remain in their projected position, while other data transmission elements are pushed into their retracted position by the annular surface of the lens mount. Thus, the data to be transmitted from the lens to the camera body is determined by the particular combination of retracted and projected data transmission elements, in other words, transmission of the data is digitally carried out. The data transmission device disclosed in U.S. Pat. No. 3,782,261, however, particularly adapted for use in a camera system employing a screw mount type coupling between a camera body and an interchangeable lens, wherein the interchangeable lens is first brought into contact with the camera body at their mount surfaces, and then turned about the optical axis thereof relative to the camera body until rigidly secured thereto. This coupling method limits the apparatus to the combination of a uniform circular array of data transmission elements with one or more arcuate slots.
Unlike the data transmission system for full open F number information of the lens suited to the screw mount type lens and camera body, an alternative data transmission system for non-screw mount type lens and camera bodies has been proposed by the assignee of the present invention in U.S. Pat. application Ser. No. 621,126, filed Oct. 9, 1975, entitled "A Totally Opened F Value information Input System of Lens for a Camera with Interchangeable Lenses". According to this application, the camera body is provided with n-switch members arranged near the mounting portion thereof for mounting a photo-taking lens to receive information representing the full open F number of the lens in the form of a coded digital information of n-bits, while each of the photographic lenses made interchangeable to the common camera body is provided with a signal pin or pins arranged near the corresponding engagement portion thereof adapted to mate with said mounting portion of the camera body to mount the lens on the camera body and capable of providing information representing the full open F number of the lens as a coded digital signal of said n-bits, whereby when the photographic lens is attached to the camera body by linear operation substantially parallel to the optical axis of the lens (that is, without rotating motion of the lens) to mate the engaging portion of the lens with the mounting portion of the camera body, the n-switch members are selectively closed by the signal pin or pins depending upon the full open F number of the lens, so that the full open F number information of the taking lens is introduced into the camera body as a coded digital information of n-bits.
In this way, more recently high speed digitalization of the single lens reflex camera system proceeds with the introduction of digital techniques. In the course of development of the digitalized camera system, the old-fashioned camera bodies and the various interchangeable lenses therefor are rendered entirely unusable. In other words, camera systems employing data transmission devices and inputting systems of the above-mentioned patent application work well only when the selection of a camera body and an interchangeable lens for establishing a complete camera with an effective exposure control system satisfies the specific design feature. For example, when the old-fashioned interchangeable lens having no provision for generating the above-mentioned signal for providing the full open F number information as a coded digital signal is combined with a camera body receptive of the full open F number information of the associated lens as a coded digital signal, the inputting of the full open F number information of the lens into the camera body cannot be entirely effected. Conversely, when the old-fashioned camera body having no provision for receiving the coded digital signal is combined with a new type interchangeable lens having the signal providing means, the inputting of the full open F number information of the lens into the camera body likewise cannot be entirely effected.
On the other hand, the presently available single lens reflex camera system is constituted from a number of different types of camera bodies in combination with a wide variety of interchangeable lenses usable in common with any one of the various camera bodies. Therefore, it is very natural that the digitalization of the camera system may begin with the camera bodies as they constitute a major portion of the system. When the digitalization is directed only to the camera bodies, however, all of the old-fashioned interchangeable lenses are made obsolete, and therefore, as the digitalization of the camera body proceeds, the necessity of providing interchangeable lenses especially adapted for use with such digitalized camera bodies arises. If the public is permitted to use the old-fashioned interchangeable lenses in combination with the digitalized camera bodies a delay in the start of digitalization would result, particularly at the interface between the camera body and the interchangeable lens mount.